(CNN) -- The bright yellow ribbons are tied tightly to the metal bars of the main gate at Danwon High School.
Nearby, they are attached to trees and posts. Altogether, there are thousands of them.
More than 300 students from the school were on a field trip on the Sewol, the ferry that sank last week off the coast of South Korea. Most of them are dead or missing.
The ribbons symbolize solidarity with the missing teenagers' families and hopes that some of the students -- who went to school in Ansan, a city near Seoul -- might still be found alive.
The approach borrows from a practice that became popular in the United States during the Iranian hostage crisis that began in 1979. The tradition was used again in the United States during the wars in Iraq and Afghanistan.
In South Korea, the ribbons have also spread into the realm of social media. Many people have posted an image evoking them as their profile photos on services like Facebook and Naver.
The image is a bold yellow square with a black border. In the center sits a simple design of a bow in black with a line of Korean written underneath.
"One small step, big miracle," it reads.
Celebrities join in
The online movement was started Saturday by a local student club, according to The Korea Herald, an English-language newspaper in South Korea.
The group wanted "to support the families of the missing and offer a hopeful message to the Korean public that the missing passengers could still be found alive," the newspaper reported.
Other variations of the yellow ribbon image have also begun to circulate on popular social media sites. And Korean celebrities have helped spread the word.
The K-pop star G-Dragon posted an image of a yellow ribbon on his Twitter feed, and the actress Park Shin-hye changed her profile picture to a ribbon picture with the popular hashtag #prayforsouthkorea written underneath.
Clusters of real ribbons have also reportedly sprung up in other cities, such as Seoul and Chuncheon. Some of the ribbons have messages and tributes written on them.
FC Seoul, a top local soccer team, will don the ribbons for a Saturday game against the Jeonnam Dragons, according to local media.
The hopes the ribbons symbolize are fading fast. Rescuers saved 174 people on April 16, the day the ship sank, but no other survivors have been found since. Divers say they have found no air pockets that could have kept people alive inside the submerged vessel.
The ribbons are also being used as a rallying point to raise money for the families who are grieving or still anxiously waiting for news of their loved ones.
National soccer player Park Chu-young, Olympic figure skater Yuna Kim and LA Dodgers pitcher Hyun-jin Ryu each donated 100 million won (roughly $100,000), according to Wow TV, a local broadcaster.
Naver, a popular Web search portal, has a yellow ribbon page allowing users to leave messages and make donations to a fund organized by the National Disaster Relief Association.
The ribbon campaign "evolved organically in the social media sphere and is the term people seem to be using in reference to all different kinds of efforts being made on behalf of the victims and families of the disaster," said Chung Seo-yoon, a representative from the association, which was founded in 1961 by media groups.
The organization is aiming to raise 500 million won. So far, tens of thousands of people have donated, raising nearly 350 million won.
In the United States, yellow ribbons were widely used to demonstrate a desire for the return of American hostages held in Tehran between 1979 and 1981.
Before that, they had been associated with convicts returning from prison.
According to the American Folklife Center at the Library of Congress, the yellow ribbon practice originated in a modern folk legend, which was turned into a popular song, "Tie a Yellow Ribbon Round the Ole Oak Tree," which was in turn transformed "into a ritual enactment."
Since the Iranian hostage crisis, it has reportedly been picked up in other countries, for a variety of movements and causes.
In its 1991 article, the American Folklife Center noted the ribbon's ability to take on new meanings:
"Ultimately, the thing that makes the yellow ribbon a genuinely traditional symbol is ... its capacity to take on new meanings, to fit new needs and, in a word, to evolve."
CNN"s Frances Cha, Andrew Stevens and Judy Kwon contributed to this report.